1. Field of the Invention
This invention relates to lubricant base stocks, which can also serve as complete lubricants in some cases; compounded lubricants, which include at least one additive for such purposes as improving high pressure and/or wear resistance, corrosion inhibition, and the like along with the lubricant base stocks which contribute the primary lubricity to the compounded lubricants; refrigerant working fluids including lubricants according to the invention along with primary heat transfer fluids, and methods for using these materials. The lubricants and lubricant base stocks are generally suitable for use with most or all halocarbon refrigerants and are particularly suitable for use with substantially chlorine-free, fluoro-group-containing organic refrigerating heat transfer fluids such as pentafluoroethane, 1,1-difluoroethane, 1,1,1-trifluroethane, and tetrafluoroethanes, most particularly 1,1,1,2-tetrafluoroethane. The lubricants and base stocks, in combination with these heat transfer fluids, are particularly suitable for lubricating compressors that operate at least part of the time at temperatures substantially higher than those at which humans can be comfortable; such compressors are generally used, for example, in vehicle air conditioning.
2. Statement of Related Art
Chlorine-free heat transfer fluids are desirable for use in refrigerant systems, because their escape into the atmosphere causes less damage to the environment than the currently most commonly used chlorofluorocarbon heat transfer fluids such as trichlorofluoromethane and dichlorodifluoromethane. The widespread commercial use of chlorine-free refrigerant heat transfer fluids has been hindered, however, by the lack of commercially adequate lubricants. This is particularly true for one of the most desirable working fluids, 1,1,1,2-tetrafluoroethane, commonly known in the art as "Refrigerant 134a" or simply "R134a". Other fluoro-substituted ethanes are also desirable working fluids.
Esters of hindered polyols, which are defined for this purpose as organic molecules containing at least five carbon atoms, at least 2 -OH groups, and no hydrogen atoms on any carbon atom directly attached to a carbon atom bearing an --OH group, have already been recognized in the art as high quality lubricant basestocks for almost any type of refrigeration machinery employing a fluorocarbon refrigerant, particularly one free from chlorine. The following patents and published patent applications also teach many general classes and specific examples of polyol esters useful as refrigerant lubricants with chlorine-free fluoro group containing heat transfer fluids: U.S. Pat. No. 4,851,144; UK 2 216 541; U.S. Pat. No. 5,021,179; U.S. Pat. No. 5,096,606; WO 90/12849 (Lubrizol); EP 0 406 479 (Kyodo Oil); EP 0 430 657 (Asahi Denka KK); EP 0 435 253 (Nippon Oil); EP 0 445 610 and 0 445 611 (Hoechst AG); EP 0449 406; EP 0 458 584 (Unichema Chemie BV); and EP 0 485 979 (Hitachi).